Deeply disappointing. I seem to be in the minority here, but I find the LR/Aperture-style interface abysmal: flat out misconceived and badly designed. Icons too small, insufficient contrast for clear signposting, and wasteful ergonomically. C1 is/used to be a model of clarity and purposefulness.
Apart from the timely abandonment of v3's Byzantine Sessions, this seems to be a downgrade in almost every way. It looks terrible, it's horrible to use and crucially it fails to add the CA and distortion correction tools now present in all its competitors.
The DR tool is a step in the right direction but everything else is bad: it's slower, uglier, not significantly better featured, and generally seems to be doing its best to encourage users to switch to Lightroom or even SilkyPix.
And they've promised no ZD support. This is one upgrade I'll be trying very hard to avoid. Forever.